Cascaded pupil-replicating waveguides

ABSTRACT

A waveguide assembly is provided. The waveguide assembly includes a pair of pupil-replicating waveguides. The first pupil-replicating waveguide is configured for receiving an input beam of image light and providing an intermediate beam comprising multiple offset portions of the input beam. The second pupil-replicating waveguide is configured for receiving the intermediate beam from the first pupil-replicating waveguide and providing an output beam comprising multiple offset portions of the intermediate beam. The input beam may be expanded by the waveguide assembly in such a manner that pupil gaps are reduced or eliminated.

TECHNICAL FIELD

The present disclosure relates to optical components, and in particularto waveguides usable in wearable displays.

BACKGROUND

Head-mounted displays (HMDs), near-eye displays (NEDs), and otherwearable display systems can be used to present virtual scenery to auser, or to augment real scenery with dynamic information, data, orvirtual objects. The virtual or augmented scenery can bethree-dimensional (3D) to enhance the experience and to match virtualobjects to real objects observed by the user. Eye position and gazedirection, and/or orientation of the user may be tracked in real time,and the displayed scenery may be dynamically adjusted depending on theuser's head orientation and gaze direction, to provide a betterexperience of immersion into a simulated or augmented environment.

Lightweight and compact near-eye displays reduce strain on the user'shead and neck, and are generally more comfortable to wear. The opticsblock of such displays can be the heaviest part of the entire system.Compact planar optical components, such as waveguides, gratings, Fresnellenses, etc., may be employed to reduce size and weight of an opticsblock. However, compact planar optics may have limitations related toimage quality, exit pupil size and uniformity, pupil swim, field of viewof the generated imagery, visual artifacts, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described in conjunction with thedrawings, in which:

FIG. 1 is a schematic side view of a near-eye display (NED) including awaveguide assembly of the present disclosure;

FIG. 2A is a side cross-sectional view of a waveguide of the waveguideassembly of FIG. 1, the waveguide including a one-dimensional (1D)diffraction grating;

FIG. 2B is a k-vector diagram illustrating beam redirection andsplitting in the waveguide of FIG. 2A;

FIG. 3A is a side cross-sectional view of a waveguide of the waveguideassembly of FIG. 1, the waveguide including a pair of 1D diffractiongratings disposed opposite one another;

FIG. 3B is a k-vector diagram illustrating beam redirection andsplitting in the waveguide of FIG. 3A;

FIG. 4A is a plan view of a waveguide of the waveguide assembly of FIG.1, the waveguide including a two-dimensional (2D) diffraction gratingincluding a pair of superimposed 1D diffraction gratings;

FIG. 4B is a k-vector diagram illustrating beam redirection andsplitting in the waveguide of FIG. 4A;

FIG. 5A is a plan view of a waveguide of the waveguide assembly of FIG.1, the waveguide including a 2D diffraction grating having a hexagonalarray of features;

FIG. 5B is a k-vector diagram illustrating beam redirection andsplitting in the waveguide of FIG. 5A;

FIG. 6A is a side cross-sectional view of an NED including cascadedwaveguide assemblies for different color channels of image light;

FIG. 6B is a side cross-sectional view of an NED including stackedwaveguide assemblies for different color channels of image light;

FIG. 7 is a flow chart of a method for expanding a beam of image lightin accordance with the present disclosure;

FIG. 8A is an isometric view of an eyeglasses form factor near-eyeaugmented reality (AR)/virtual reality (VR) display incorporating awaveguide assembly of the present disclosure;

FIG. 8B is a side cross-sectional view of the AR/VR display of FIG. 8A;and

FIG. 9 is an isometric view of a head-mounted display (HMD)incorporating a waveguide assembly of the present disclosure.

DETAILED DESCRIPTION

While the present teachings are described in conjunction with variousembodiments and examples, it is not intended that the present teachingsbe limited to such embodiments. On the contrary, the present teachingsencompass various alternatives and equivalents, as will be appreciatedby those of skill in the art. All statements herein reciting principles,aspects, and embodiments of this disclosure, as well as specificexamples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents as well asequivalents developed in the future, i.e., any elements developed thatperform the same function, regardless of structure.

As used herein, the terms “first”, “second”, and so forth are notintended to imply sequential ordering, but rather are intended todistinguish one element from another, unless explicitly stated.Similarly, sequential ordering of method steps does not imply asequential order of their execution, unless explicitly stated.

A pupil-replicating waveguide may be used to carry an image from aprojector to an eye of a user. A high degree of flatness and parallelismof waveguide surfaces is required to maintain good quality of theobserved image. It is easier to polish a thicker optical component, suchas a waveguide, to high flatness and parallelism. However, a thickerpupil-replicating waveguides may have areas of output pupil where imagebrightness sharply drops due to so-called gaps or holes in the outputpupil. The gaps may appear due to larger lateral offsets of the imagebeam upon reflection from outer surfaces of a thicker waveguide. Inaccordance with the present disclosure, the output pupil gaps may bereduced or even completely eliminated by providing an additionalpupil-replicating waveguide upstream of the thicker waveguide. Theadditional waveguide may expand the input beam enough to close theoutput pupil gaps of the thicker waveguide.

In accordance with the present disclosure, there is provided a waveguideassembly comprising cascaded first and second pupil-replicatingwaveguides. The first pupil-replicating waveguide is configured forreceiving a first input beam of image light and providing a firstintermediate beam comprising multiple offset portions of the first inputbeam, and the second pupil-replicating waveguide is configured forreceiving the first intermediate beam from the first pupil-replicatingwaveguide and providing a first output beam comprising multiple offsetportions of the first intermediate beam. The first pupil-replicatingwaveguide has a first replication offset between the multiple offsetportions of the first input beam, and the second pupil-replicatingwaveguide has a second replication offset between the multiple offsetportions of the first intermediate beam; the first replication offsetmay be smaller than the second replication offset.

In some embodiments, a spot size of the first intermediate beam isgreater than a spot size of the first input beam, but less than twicethe spot size of the first input beam. The first pupil-replicatingwaveguide may include a first substrate comprising first and secondsurfaces for propagating the first input beam in the first substrate byreflecting the first input beam from the first and second surfaces ofthe first substrate, and a first diffraction grating supported by thefirst substrate in an optical path of the first input beam andconfigured for diffracting the first input beam impinging thereon forproviding the multiple offset portions of the first input beam. In someembodiments, the first diffraction grating includes a first plurality ofgrating lines running parallel to one another and a second plurality ofgrating lines running parallel to one another and at an angle to thegrating lines of the first plurality. In some embodiments, the firstdiffraction grating includes a two-dimensional array of features fordiffracting the first input beam in first and second non-paralleldirections.

The second pupil-replicating waveguide may include a second substratecomprising first and second surfaces for propagating the firstintermediate beam in the second substrate by reflecting the firstintermediate beam from the first and second surfaces of the secondsubstrate, and a second diffraction grating supported by the secondsubstrate in an optical path of the first intermediate beam andconfigured for diffracting the first intermediate beam impinging thereonfor providing the multiple offset portions of the first intermediatebeam. The first pupil-replicating waveguide may further include a thirddiffraction grating supported by the first substrate in the optical pathof the first input beam and configured for diffracting the first inputbeam impinging thereon for at least one of splitting or redirecting thefirst input beam.

In some embodiments, the waveguide further includes cascaded third andfourth pupil-replicating waveguides. The third pupil-replicatingwaveguide may be configured for receiving a second input beam of theimage light and providing a second intermediate beam comprising multipleoffset portions of the second input beam. The fourth pupil-replicatingwaveguide may be configured for receiving the second intermediate beamfrom the third pupil-replicating waveguide and providing a second outputbeam comprising multiple offset portions of the second intermediatebeam.

The waveguide may further include cascaded fifth and sixthpupil-replicating waveguides. The fifth pupil-replicating waveguide maybe configured for receiving a third input beam of the image light andproviding a third intermediate beam comprising multiple offset portionsof the third input beam. The sixth pupil-replicating waveguide may beconfigured for receiving the third intermediate beam from the fifthpupil-replicating waveguide and providing a third output beam comprisingmultiple offset portions of the third intermediate beam. The first,second, and third input beams may include first, second, and third colorchannels of the image light, respectively.

The second, fourth, and sixth pupil-replicating waveguides may bedisposed in a stack configuration. The fourth pupil-replicatingwaveguide may be configured for propagating the first output beamtherethrough substantially without reflecting the first output beamtherein. The sixth pupil-replicating waveguide may be configured forpropagating the first and second output beams therethrough substantiallywithout reflecting the first and second output beams therein.

In accordance with the present disclosure, there is provided a near-eyedisplay (NED) comprising a first light source for providing a firstinput beam of image light, and first and second pupil-replicatingwaveguides. The first pupil-replicating waveguide is configured forreceiving the first input beam and providing a first intermediate beamcomprising multiple offset portions of the first input beam. The secondpupil-replicating waveguide is configured for receiving the firstintermediate beam from the first pupil-replicating waveguide andproviding a first output beam comprising multiple offset portions of thefirst intermediate beam. In some embodiments, the secondpupil-replicating waveguide is thicker than the first pupil-replicatingwaveguide, and/or the second pupil-replicating waveguide is longer thanthe first pupil-replicating waveguide in a direction of offset of themultiple offset portions of the first intermediate beam in the secondpupil-replicating waveguide.

In some embodiments, the NED further includes second and third lightsources for providing second and third input beams of image light,respectively. The first, second, and third input beams comprise first,second, and third color channels of the image light. The NED may furtherinclude cascaded third and fourth pupil-replicating waveguides. Thethird pupil-replicating waveguide may be configured for receiving thesecond input beam of the image light and providing a second intermediatebeam comprising multiple offset portions of the second input beam. Thefourth pupil-replicating waveguide may be configured for receiving thesecond intermediate beam from the second pupil-replicating waveguide andproviding a second output beam comprising multiple offset portions ofthe second intermediate beam. The NED may further include cascaded fifthand sixth pupil-replicating waveguides. The fifth pupil-replicatingwaveguide may be configured for receiving the third input beam of theimage light and providing a third intermediate beam comprising multipleoffset portions of the third input beam. The sixth pupil-replicatingwaveguide may be configured for receiving the third intermediate beamfrom the fifth pupil-replicating waveguide and providing a third outputbeam comprising multiple offset portions of the third intermediate beam.

In some embodiments, the second, fourth, and sixth pupil-replicatingwaveguides are disposed in a stack configuration. The fourthpupil-replicating waveguide may be configured for propagating the firstoutput beam therethrough substantially without reflecting the firstoutput beam therein. The sixth pupil-replicating waveguide may beconfigured for propagating the first and second output beamstherethrough substantially without reflecting the first and secondoutput beams therein.

In accordance with the present disclosure, there is further provided amethod for expanding an input beam of image light. The method includespropagating the input beam in a first pupil-replicating waveguide toobtain an intermediate beam comprising multiple offset portions of theinput beam, and propagating the intermediate beam in a secondpupil-replicating waveguide to obtain an output beam comprising multipleoffset portions of the intermediate beam. A replication offset betweenthe multiple offset portions of the input beam may be smaller than areplication offset between the multiple offset portions of theintermediate beam. The multiple offset portions of the input beam in thefirst pupil-replicating waveguide may be offset in first and secondnon-parallel directions.

Referring now to FIG. 1, a near-eye display (NED) 120 includes a lightsource 181 for providing an input beam 110 of image light to a waveguideassembly 100. The image light may include an image in angular domain, tobe presented to a user for a direct observation, i.e. without projectingon a screen. The waveguide assembly 100 includes cascaded first 101 andsecond 102 pupil-replicating waveguides. The first pupil-replicatingwaveguide 101 is configured for receiving the input beam 110 andproviding an intermediate beam 111 including multiple offset portions,e.g. portions 104 (dotted lines), 105 (short-dash lines), 106 (long-dashlines) of the input beam 110 at an exit pupil 107 of the firstpupil-replicating waveguide 101. The second pupil-replicating waveguide102 is configured for receiving the intermediate beam 111 from the firstpupil-replicating waveguide 101 and providing an output beam 112including multiple offset portions 114, 115, 116, 117, 118, and 119 ofthe first intermediate beam 101 at an exit pupil 130 of the secondpupil-replicating waveguide 102.

In the embodiment shown in FIG. 1, the first pupil-replicating waveguide101 includes a first substrate 121 having opposed first 131 and second132 optical surfaces. In operation, the input beam 110 propagates in thefirst substrate 121 by reflecting, e.g. by total internal reflection(TIR), from the first 131 and second 132 optical surfaces in a zigzagmanner, forming a first optical path 126 shown with dotted lines. It isto be noted that the input beam 110 may propagate both to the left andto the right in FIG. 1, as illustrated. A first diffraction grating 141(thick dashed line) may be supported by the first substrate 121 in thefirst optical path 126 of the input beam 110 and configured fordiffracting the input beam 110 impinging onto the first diffractiongrating 141, as illustrated with dotted-line rays 127, for providing thecorresponding mutually offset portions 104, 105, 106 of the input beam110.

The second pupil-replicating waveguide 102 may include a secondsubstrate 122 having opposed first 151 and second 152 optical surfaces.In operation, the intermediate beam 111 propagates in the secondsubstrate 122 by zigzag reflections from its first 151 and second 152surfaces, forming a second optical path 128 (dotted lines), optionallyextending both to the left and to the right in FIG. 1, as shown. Asecond diffraction grating 142 (thick dashed line) may be supported bythe second substrate 122 in the second optical path 128 of theintermediate beam 111 and configured for diffracting the intermediatebeam 111 impinging onto the second diffraction grating 142, asillustrated with dotted-line rays 129, thus providing the multipleoffset portions 114-119 of the intermediate beam 111.

An advantage brought by introducing the first pupil-replicatingwaveguide 101 into the waveguide assembly 100 may be illustrated byinitially considering optical performance of the waveguide assembly 100without the first pupil-replicating waveguide 101. If the firstpupil-replicating waveguide 101 were absent, then the secondpupil-replicating waveguide 102 would receive only one of the replicatedportions 104-106, specifically the leftmost portion 104 (shown in dottedlines). The second pupil-replicating waveguide 102 would then replicatethe leftmost portion 104, providing a second portion 104′; however thesetwo portions, 104 and 104′, would be separated by a pupil gap 113, andaccordingly, an eye would receive no image when placed in the pupil gap113. Advantageously, the first pupil-replicating waveguide 101 fills thepupil gap 113 by providing the other replicated beam portions 105 and106. In other words, the first pupil-replicating waveguide 101 fills thepupil gaps by expanding the input beam 110 before it enters the secondpupil-replicating waveguide 102. This allows the secondpupil-replicating waveguide 102 to be made thicker and thus easier tomanufacture to a required degree of flatness and parallelism across theentire length of the second pupil-replicating waveguide 102. Among otherthings, the increased thickness enables the second substrate 122 to alsobe more mechanically stable.

A replication offset between the multiple offset portions 104-106 of theinput beam 110 provided by the first pupil-replicating waveguide 101 mayremain relatively small; for example, the replication offset may remainsmaller than a replication offset between the multiple offset portions114-119 of the intermediate beam 111 provided by the secondpupil-replicating waveguide 102. The smaller replication offset of thefirst pupil-replicating waveguide 101 may be due to a smaller thicknessof the first pupil-replicating waveguide 101, a smaller angulardispersion of the first diffraction grating 141, or both, as compared tothe thickness of the second pupil-replicating waveguide 102 and theangular dispersion of the second diffraction grating 142, respectively.The smaller thickness and/or the angular dispersion of the firstpupil-replicating waveguide 101 enables first pupil-replicatingwaveguide 101 to support a portion of the FOV supported by the secondpupil replicating waveguide 102. In one embodiment, a spot size of theintermediate beam 111 is greater than a spot size of the input beam 110,but less than twice the spot size of the input beam 110. It may bedesirable to reduce a distance between the first 101 and second 102pupil-replicating waveguides to reduce the height of the assembly;however it is to be noted that the first 101 and second 102pupil-replicating waveguides should not optically contact each other, toavoid affecting TIR in these waveguides, if used. A plurality ofspacers, e.g. glass beads of at least 3-4 micrometers in diameter, maybe placed on the perimeter of the first pupil-replicating waveguide 101to ensure a fixed spaced apart relationship between the first 101 andsecond 102 pupil-replicating waveguides.

Examples of configuring the first 101 and second 102 pupil-replicatingwaveguides for receiving a beam of light and providing multiple offsetbeam portions of the beam will now be considered. Referring first toFIG. 2A, a waveguide 200 is an embodiment of the first waveguide 101 ofFIG. 1, the second waveguide 102, or both. The waveguide 200 of FIG. 2Aincludes a surface-relief grating (SRG) 241 supported by a substrate221. The SRG 241 is a one-dimensional (1D) grating, that is, it includesa plurality of grooves running parallel to each other for diffracting abeam of light in a plurality of directions in a single plane. Inoperation, a first input ray 110R propagates through the substrate 221providing the leftmost beam portion 104, as well as diffracts on the SRG241 in the plane of FIG. 2A. The diffraction redirects the first inputray 110R to reflect from inside the substrate 221 by TIR, forming azigzag optical path 226. Upon each encounter with the SRG 241, the firstinput ray 110R diffracts, producing the center 105 and the rightmost 106portions of the intermediate beam 111. The beam diffraction andredirection is schematically represented in FIG. 2B, which shows left251 and right 252 halves of a field of view (FOV) of the image to bedisplayed, and corresponding angular areas 253 and 254 for angles ofdiffracted light within a donut-shaped area 255 representing an angularrange where the beam propagation effectively occurs by TIR in thesubstrate 221. The initial diffraction of the first input ray 110R(dotted lines) is represented by a first forward k-vector 261 of FIG.2B, and a subsequent diffraction, i.e. the diffraction which out-couplesthe corresponding beam portions 105 and 106 is represented by a firstreverse k-vector 263 of equal magnitude and opposite direction, suchthat an original direction of the beam portions 105 and 106 ispreserved. For a second input ray 110L (dashed lines) propagating to theleft in FIG. 2A, the initial diffraction is represented by a secondforward k-vector 262 of FIG. 2B, and a subsequent out-couplingdiffraction is represented by a second reverse k-vector 264 of equalmagnitude and opposite direction.

Referring to FIG. 3A, a waveguide 300 is an embodiment of the firstwaveguide 101 and/or the second waveguide 102 of FIG. 1. The waveguide300 of FIG. 3A may include at least two diffraction gratings, i.e. thefirst waveguide 101, the second waveguide 102, or both the first 101 andsecond 102 waveguides may include at least two diffraction gratings. Inthe embodiment shown, the waveguide 300 includes three diffractiongratings: an in-coupling grating 341, a redirecting grating 342, and anout-coupling grating 343, all 1D diffraction gratings supported by asubstrate 321 in an optical path 326 of the first input ray 110R. Thein-coupling grating 341 diffracts impinging first input ray 110R topropagate in the substrate 321 by TIR, and the redirecting grating 342diffracts the impinging first input ray 110R into +1^(st) and −1^(st)diffraction orders, thereby splitting and redirecting the first inputray 110R, the portions of which 105, 106 are then out-coupled bydiffracting on the out-coupling grating 343. The second input ray 110Lis not shown in FIG. 3A for brevity.

This process of diffraction and redirection is schematically illustratedin a k-vector diagram of FIG. 3B showing two possible paths ofpropagation of the first input ray 110R in the substrate 321 (FIG. 3A)along with corresponding angular areas representing the angular rangefor each particular beam path. In a first path illustrated by dottedlines, a first k-vector 361 (FIG. 3B) associated with a first field ofview portion 351 corresponds to diffraction on the in-coupling grating341, with angles of resulting rays landing within a second angular area352. The redirecting grating 342 redirects the landed rays to a thirdangular area 353 by diffracting into a +1^(st) diffraction order asrepresented by a second k-vector 362. Then, the out-coupling grating 343diffracts the rays out at the same angles as corresponding input rays,as represented by a third k-vector 363, forming the beam portions 105and 106. The beam redirection along a second path, illustrated withdashed lines, corresponds to diffraction into a −1^(st) diffractionorder, and otherwise occurs similarly. The second path beam redirectionis represented by a second field of view portion 354, fourth 364, fifth365, and sixth 366 k-vectors, and corresponding angular areas 355 and356.

Turning to FIG. 4A, a waveguide 400 is an embodiment of the firstwaveguide 101 and/or the second waveguide 102 of FIG. 1. The waveguide400 of FIG. 4A includes a two-dimensional (2D) diffraction gratinghaving a first plurality of grating lines 441 running parallel to oneanother, and a second plurality of grating lines 442 running parallel toone another and at an angle to the grating lines 441 of the firstplurality. The two nonparallel pluralities of grating lines 441 and 442form a 2D pattern for diffracting a beam of light in two non-paralleldirections. In the embodiment shown in FIG. 4A, first 441 and second 442pluralities of grating lines are perpendicular to each other, forming arectangular pattern of features for diffracting the rays up-down andleft-right. The angular dispersions of the first diffraction grating maybe different in the two non-parallel directions of diffraction, asshown. A corresponding k-vector diagram of FIG. 4B includes four pairsof k-vectors, a first pair 461-462, a second pair 463-464, a third pair465-466, and a fourth pair 467-468. The resulting field of view is shownat 450, and four surrounding angular areas corresponding to the k-vectorpairs are shown at 451, 452, 453, and 454.

Referring now to FIG. 5A, a waveguide 500 can be used for the firstwaveguide 101 and/or the second waveguide 102 of FIG. 1. The waveguide500 of FIG. 5 is similar to the waveguide 400 of FIG. 4, but includes ahexagonal 2D array of features 541 forming a 2D diffraction grating fordiffracting a beam of light in three planes at 120 degrees to eachother. A corresponding k-vector diagram of FIG. 5B includes six pairs ofk-vectors, a first pair 561-562, a second pair 563-564, a third pair565-566, a fourth pair 567-568, a fifth pair 569-570, and a sixth pair571-572. The resulting field of view is shown at 550, and sixsurrounding angular areas corresponding to the k-vector pairs are shownat 551, 552, 553, 554, 555, and 556. It is further noted that thediffraction gratings shown in FIGS. 2A-5A may include SRGs, volume Bragggratings (VBGs), polarization volume gratings, etc. The gratings may bedisposed proximate the outer surfaces or inside (e.g. in the middle) ofrespective substrates.

Referring to FIG. 6A, an NED 620 includes first 681, second 682, andthird 683 light sources providing first 610, second 613, and third 616input beams of image light, respectively, each beam carrying a dedicatedcolor channel, e.g. red, green, and blue color channel of image light tobe carried to a user's eye. The image light may include an image inangular domain to be presented to a user for a direct observation, i.e.without projecting the image on a screen. To carry the image, the NED620 includes a cascaded waveguide assembly 600A comprising three pairsof pupil-replicating waveguides, each light source being opticallycoupled to a particular pair of pupil-replicating waveguides carryinglight of a particular color channel. For example, a first pair includesfirst 601 and second 602 cascaded pupil-replicating waveguides. Thefirst pupil-replicating waveguide 601 is configured to receive the firstinput beam 610 of image light from the first light source 681 comprisingthe first color channel. The first pupil-replicating waveguide 601provides a first intermediate beam 611 comprising multiple offsetportions of the first input beam 610, similarly to the waveguideassembly 100 of FIG. 1. The second pupil-replicating waveguide 602 isconfigured for receiving the first intermediate beam 611 from the firstpupil-replicating waveguide 601 and providing a first output beam 612(long-dash arrows) comprising multiple offset portions of the firstintermediate beam 611, similarly to NED 120 of FIG. 1. To that end, thefirst 601 and second 602 pupil-replicating waveguides can be based onthe waveguides 200 of FIG. 2A, 300 of FIG. 3A, 400 of FIG. 4A, and/or500 of FIG. 5A.

A second pair of pupil-replicating waveguides of the waveguide assembly100 includes cascaded third 603 and fourth 604 pupil-replicatingwaveguides. The third pupil-replicating waveguide 603 is configured forreceiving the second input beam 613 of the image light and providing asecond intermediate beam 614 comprising multiple offset portions of thesecond input beam 613. The fourth pupil-replicating waveguide 604 isconfigured for receiving the second intermediate beam 614 from the thirdpupil-replicating waveguide 603 and providing a second output beam 615(short-dash arrows) comprising multiple offset portions of the secondintermediate beam 614. In a similar manner, a third pair ofpupil-replicating waveguides includes cascaded fifth 605 and sixth 606pupil-replicating waveguides. The fifth pupil-replicating waveguide 605is configured for receiving the third input beam 616 of the image lightand providing a third intermediate beam 617 comprising multiple offsetportions of the third input beam 616. The sixth pupil-replicatingwaveguide 606 is configured for receiving the third intermediate beam617 from the fifth pupil-replicating waveguide 605 and providing a thirdoutput beam 618 (dotted-line arrows) comprising multiple offset portionsof the third intermediate beam 617. The third 603, fourth 604, fifth605, and sixth 606 pupil-replicating waveguides can be based on thewaveguides 200 of FIG. 2A, 300 of FIG. 3A, 400 of FIG. 4A, and/or 500 ofFIG. 5A.

In the embodiment shown in FIG. 6A, the second 602, fourth 604, andsixth 606 pupil-replicating waveguides are disposed in a stackconfiguration, that is, stacked together, with a small gap in between.The first 601, third 603, and fifth 605 pupil-replicating waveguides maybe supported by the second 602, fourth 604, and sixth 606pupil-replicating waveguides on a side of the respective waveguides 602,604, and 606, the third pupil-replicating waveguide 603 being disposedadjacent the second pupil-replicating waveguide 602, and the fifthpupil-replicating waveguide 605 being disposed adjacent the fourthpupil-replicating waveguide 604, as shown. The fourth pupil-replicatingwaveguide 604 can be configured for propagating the first output beam612 directly through the thickness of the fourth pupil-replicatingwaveguide 604, such that the first output beam 612 is not redirected topropagate in the fourth pupil-replicating waveguide 604 by internalreflections from its surfaces. Similarly, the sixth pupil-replicatingwaveguide 606 is configured for propagating the first 612 and second 615output beams directly through the thickness of the sixthpupil-replicating waveguide 606, such that the first 612 and second 615output beams are not redirected to propagate in the sixthpupil-replicating waveguide 606 by internal reflections. The second 602,fourth 604, and sixth 606 pupil-replicating waveguides are fixed in aspaced-apart relationship to prevent optical contact between thewaveguides, to make sure that the TIR of the output beams 612, 615, and618 is not affected. Glass beads of a suitable diameter, or otherspacers of a controlled size may be used for this purpose. Thewaveguides of individual waveguide pairs, that is, 601-602, 603-604, and605-606 may also need to be separated at some minimal distance, for asame reason of making sure the TIR in the waveguides is not affected.

Turning to FIG. 6B, an NED 620B is similar to the NED 620A of FIG. 6A.The NED 620B includes a stacked waveguide assembly 600B having the first601, third 603, and fifth 605 pupil-replicating waveguides stackedtogether, and the second 602, fourth 604, and sixth 606pupil-replicating waveguides stacked together, forming a stackedwaveguide assembly 600B. The first 601 and second 602 pupil-replicatingwaveguides are configured to expand the beam of the first color channel,the third 603 and fourth 604 pupil-replicating waveguides are configuredto expand the beam of the second color channel, and the fifth 605 andsixth 606 pupil-replicating waveguides are configured to expand the beamof the third color channel. A single multi-colored light source 684provides beams 612, 615, and 618 corresponding to different colorchannels.

Turning to FIG. 7, a method 700 for expanding an input beam of imagelight includes propagating (702) the input beam of image light in afirst pupil-replicating waveguide, e.g. the pupil-replicating waveguide101 of FIG. 1, to obtain an intermediate beam comprising multiple offsetportions of the input beam. The intermediate beam is coupled (704 inFIG. 7) to a second pupil-replicating waveguide, e.g. the secondpupil-replicating waveguide 102 of FIG. 1, and is propagated (706 inFIG. 7) in the second pupil-replicating waveguide to obtain an outputbeam comprising multiple offset portions of the intermediate beam. Insome embodiments, a replication offset between the multiple offsetportions of the input beam is smaller than a replication offset betweenthe multiple offset portions of the intermediate beam. This enables oneto make the second pupil-replicating waveguide thicker and/or longerwith good flatness and parallelism of TIR surfaces. The replicationoffset may occur independently in two dimensions; in other words, themultiple offset portions of the input beam in the first replicatingwaveguide may be independently offset in first and second non-paralleldirections, by different amounts if required. This provides flexibilityin filling pupil gaps in X and Y directions in the plane of an eyebox ofa visual display.

Referring to FIGS. 8A and 8B, a near-eye augmented reality (AR)/virtualreality (VR) display 800 includes a body or frame 802 having a formfactor of a pair of eyeglasses. A display 804 includes a waveguideassembly 806 (FIG. 8B), which provides image light 808 to an eyebox 810,i.e. a geometrical area where a good-quality image may be presented to auser's eye 812. The waveguide assembly 806 may include any of thewaveguide assemblies described herein, e.g. the waveguide assembly 100of FIG. 1 and/or the waveguide assemblies 600A, 600B of FIGS. 6A, 6B.

An image light source of the near-eye AR/VR display 800 may include, forexample and without limitation, a liquid crystal display (LCD), anorganic light emitting display (OLED), an inorganic light emittingdisplay (ILED), an active-matrix organic light-emitting diode (AMOLED)display, a transparent organic light emitting diode (TOLED) display, aprojector, or a combination thereof. The near-eye AR/VR display 800 mayfurther include an eye-tracking system 814 for determining, in realtime, the gaze direction and/or the vergence angle of the user's eyes812. The determined gaze direction and vergence angle may also be usedfor real-time compensation of visual artifacts dependent on the angle ofview and eye position. Furthermore, the determined vergence and gazeangles may be used for interaction with the user, highlighting objects,bringing objects to the foreground, dynamically creating additionalobjects or pointers, etc. Yet furthermore, the near-eye AR/VR display800 may include an audio system, such a set of small speakers orheadphones, not shown.

Turning now to FIG. 9, an HMD 900 is an example of an AR/VR wearabledisplay system enclosing user's eyes for a greater degree of immersioninto the AR/VR environment. The HMD 900 may be a part of an AR/VR systemincluding a user position and orientation tracking system, an externalcamera, a gesture recognition system, control means for providing userinput and controls to the system, and a central console for storingsoftware programs and other data for interacting with the user forinteracting with the AR/VR environment. The functional purpose of theHMD 900 is to augment views of a physical, real-world environment withcomputer-generated imagery, and/or to generate entirely virtual 3Dimagery. The HMD 900 may include a front body 902 and a band 904. Thefront body 902 is configured for placement in front of eyes of the userin a reliable and comfortable manner, and the band 904 may be stretchedto secure the front body 902 on the user's head. A display system 980may include any of the waveguide assemblies described herein. Thedisplay system 980 may be disposed in the front body 902 for presentingAR/VR images to the user. Sides 906 of the front body 902 may be opaqueor transparent.

In some embodiments, the front body 902 includes locators 908, aninertial measurement unit (IMU) 910 for tracking acceleration of the HMD900 in real time, and position sensors 912 for tracking position of theHMD 900 in real time. The locators 908 may be traced by an externalimaging device of a virtual reality system, such that the virtualreality system can track the location and orientation of the HMD 900 inreal time. Information generated by the IMU and the position sensors 912may be compared with the position and orientation obtained by trackingthe locators 908, for improved tracking of position and orientation ofthe HMD 900. Accurate position and orientation is important forpresenting appropriate virtual scenery to the user as the latter movesand turns in 3D space.

The HMD 900 may further include an eye tracking system 914, whichdetermines orientation and position of user's eyes in real time. Theobtained position and orientation of the eyes allows the HMD 900 todetermine the gaze direction of the user and to adjust the imagegenerated by the display system 980 accordingly. In one embodiment, thevergence, that is, the convergence angle of the user's eyes gaze, isdetermined. The determined gaze direction and vergence angle may be usedfor real-time compensation of visual artifacts dependent on the angle ofview and eye position. Furthermore, the determined vergence and gazeangles may be used for interaction with the user, highlighting objects,bringing objects to the foreground, creating additional objects orpointers, etc. An audio system may also be provided including e.g. a setof small speakers built into the front body 902.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Other various embodiments andmodifications, in addition to those described herein, will be apparentto those of ordinary skill in the art from the foregoing description andaccompanying drawings. Such other embodiments and modifications areintended to fall within the scope of the present disclosure. Further,although the present disclosure has been described herein in the contextof a particular implementation in a particular environment for aparticular purpose, those of ordinary skill in the art will recognizethat its usefulness is not limited thereto and that the presentdisclosure may be beneficially implemented in any number of environmentsfor any number of purposes. Accordingly, the claims set forth belowshould be construed in view of the full breadth and spirit of thepresent disclosure as described herein.

What is claimed is:
 1. A waveguide assembly comprising cascaded firstand second pupil-replicating waveguides, wherein the firstpupil-replicating waveguide is configured for receiving a first inputbeam of image light and providing a first intermediate beam comprisingmultiple offset portions of the first input beam, and wherein the secondpupil-replicating waveguide is configured for receiving the firstintermediate beam from the first pupil-replicating waveguide andproviding a first output beam comprising multiple offset portions of thefirst intermediate beam.
 2. The waveguide assembly of claim 1, whereinthe first pupil-replicating waveguide has a first replication offsetbetween the multiple offset portions of the first input beam; whereinthe second pupil-replicating waveguide has a second replication offsetbetween the multiple offset portions of the first intermediate beam; andwherein the first replication offset is smaller than the secondreplication offset.
 3. The waveguide assembly of claim 1, wherein a spotsize of the first intermediate beam is greater than a spot size of thefirst input beam, but less than twice the spot size of the first inputbeam.
 4. The waveguide assembly of claim 1, wherein the firstpupil-replicating waveguide comprises: a first substrate comprisingfirst and second surfaces for propagating the first input beam in thefirst substrate by reflecting the first input beam from the first andsecond surfaces of the first substrate; and a first diffraction gratingsupported by the first substrate in an optical path of the first inputbeam and configured for diffracting the first input beam impingingthereon for providing the multiple offset portions of the first inputbeam.
 5. The waveguide assembly of claim 4, wherein the firstdiffraction grating comprises a first plurality of grating lines runningparallel to one another and a second plurality of grating lines runningparallel to one another and at an angle to the grating lines of thefirst plurality.
 6. The waveguide assembly of claim 4, wherein the firstdiffraction grating comprises a two-dimensional array of features fordiffracting the first input beam in first and second non-paralleldirections.
 7. The waveguide assembly of claim 4, wherein the secondpupil-replicating waveguide comprises: a second substrate comprisingfirst and second surfaces for propagating the first intermediate beam inthe second substrate by reflecting the first intermediate beam from thefirst and second surfaces of the second substrate; and a seconddiffraction grating supported by the second substrate in an optical pathof the first intermediate beam and configured for diffracting the firstintermediate beam impinging thereon for providing the multiple offsetportions of the first intermediate beam.
 8. The waveguide assembly ofclaim 7, wherein the second substrate is longer than the first substratein a direction of offset of the multiple offset portions of the firstintermediate beam in the second substrate.
 9. The waveguide assembly ofclaim 7, wherein at least one of: the second substrate is thicker thanthe first substrate; or the second diffraction grating has a largerangular dispersion than the first diffraction grating.
 10. The waveguideassembly of claim 7, wherein the first diffraction grating comprises afirst surface relief grating (SRG), and wherein the second diffractiongrating comprises a second SRG.
 11. The waveguide assembly of claim 4,wherein the first pupil-replicating waveguide further comprises a thirddiffraction grating supported by the first substrate in the optical pathof the first input beam and configured for diffracting the first inputbeam impinging thereon for at least one of splitting or redirecting thefirst input beam.
 12. The waveguide assembly of claim 1, furthercomprising: cascaded third and fourth pupil-replicating waveguides,wherein the third pupil-replicating waveguide is configured forreceiving a second input beam of the image light and providing a secondintermediate beam comprising multiple offset portions of the secondinput beam, and wherein the fourth pupil-replicating waveguide isconfigured for receiving the second intermediate beam from the thirdpupil-replicating waveguide and providing a second output beamcomprising multiple offset portions of the second intermediate beam; andcascaded fifth and sixth pupil-replicating waveguides, wherein the fifthpupil-replicating waveguide is configured for receiving a third inputbeam of the image light and providing a third intermediate beamcomprising multiple offset portions of the third input beam, and whereinthe sixth pupil-replicating waveguide is configured for receiving thethird intermediate beam from the fifth pupil-replicating waveguide andproviding a third output beam comprising multiple offset portions of thethird intermediate beam; wherein the first, second, and third inputbeams comprise first, second, and third color channels of the imagelight, respectively.
 13. The waveguide assembly of claim 12, wherein thesecond, fourth, and sixth pupil-replicating waveguides are disposed in astack configuration; wherein the fourth pupil-replicating waveguide isconfigured for propagating the first output beam therethroughsubstantially without reflecting the first output beam therein; andwherein the sixth pupil-replicating waveguide is configured forpropagating the first and second output beams therethrough substantiallywithout reflecting the first and second output beams therein.
 14. Anear-eye display (NED) comprising: a first light source for providing afirst input beam of image light; a first pupil-replicating waveguideconfigured for receiving the first input beam and providing a firstintermediate beam comprising multiple offset portions of the first inputbeam; and a second pupil-replicating waveguide configured for receivingthe first intermediate beam from the first pupil-replicating waveguideand providing a first output beam comprising multiple offset portions ofthe first intermediate beam.
 15. The NED of claim 14, wherein at leastone of: the second pupil-replicating waveguide is thicker than the firstpupil-replicating waveguide; or the second pupil-replicating waveguideis longer than the first pupil-replicating waveguide in a direction ofoffset of the multiple offset portions of the first intermediate beam inthe second pupil-replicating waveguide.
 16. The NED of claim 14, furthercomprising: second and third light sources for providing second andthird input beams of image light, respectively, wherein the first,second, and third input beams comprise first, second, and third colorchannels of the image light; cascaded third and fourth pupil-replicatingwaveguides, wherein the third pupil-replicating waveguide is configuredfor receiving the second input beam of the image light and providing asecond intermediate beam comprising multiple offset portions of thesecond input beam, and wherein the fourth pupil-replicating waveguide isconfigured for receiving the second intermediate beam from the thirdpupil-replicating waveguide and providing a second output beamcomprising multiple offset portions of the second intermediate beam; andcascaded fifth and sixth pupil-replicating waveguides, wherein the fifthpupil-replicating waveguide is configured for receiving the third inputbeam of the image light and providing a third intermediate beamcomprising multiple offset portions of the third input beam, and whereinthe sixth pupil-replicating waveguide is configured for receiving thethird intermediate beam from the fifth pupil-replicating waveguide andproviding a third output beam comprising multiple offset portions of thethird intermediate beam.
 17. The NED of claim 16, wherein the second,fourth, and sixth pupil-replicating waveguides are disposed in a stackconfiguration; wherein the fourth pupil-replicating waveguide isconfigured for propagating the first output beam therethroughsubstantially without reflecting the first output beam therein; andwherein the sixth pupil-replicating waveguide is configured forpropagating the first and second output beams therethrough substantiallywithout reflecting the first and second output beams therein.